* doc/autoconf.texi:

* doc/autoconf.texi:
(Installation Directory Variables, Build Directories):
(Automatic Remaking, Subdirectories, Fortran Compiler):
(Making testsuite Scripts, Defining Directories):
Quote variable usages better.
(Installation Directory Variables): Fix table item font.
Reword slightly to clarify.  Generalize advice about
not using special characters to include all file-related
vars, not just VPATH.
(Special Chars in Variables): Warn about special characters in
$(srcdir) too.
(Assignments): Clarify default-value example as suggested by
Ralf Wildenhues in
<http://lists.gnu.org/archive/html/autoconf-patches/2006-06/msg00072.html>.
(Special Shell Variables): Note leading ./ or ../, as suggested
by Stepan Kasal.
(Limitations of Builtins): Under cd, warn about CDPATH.
(The Make Macro MAKEFLAGS): Untabify.  Problem reported by
Ralf Wildenhues.